TypeScript Will Kill CoffeeScript and Dart!

TypeScript is a superset of JavaScript that combines type checking and static analysis, explicit interfaces, and best practices into a single language and compiler.

Since it's a superset of JavaScript, any JavaScript code is also a valid TypeScript code. It's also open source! The designer is Anders Hejlsberg (born 1960), father of Turbo Pascal, Delphi, Microsoft C#.